1. Field of the Invention
The present invention relates to a process for the removal of water soluble organic compounds from water. The invention further relates to a process for the removal of water soluble organic compounds associated with the production of crude oil. The invention further relates to a means of recovery of the soluble organic compounds present in produced water.
2. Description of the Related Art
In the process of crude oil production from subterranean formations, a substantial amount of water may be produced. Such oil-associated water (produced water) contains contaminating compounds which must be removed prior to releasing the water into the environment. Of course, it is possible to use turbidometric or colorimetric procedures to test for the content of oil in such water. However, in many instances, the contamination in the water is not visible to the naked eye since many of the pollutants are water soluble and, therefore, require detection methods capable of monitoring these compounds. For example, Environmental Protection Agency regulations currently stipulate a maximum oil content of 48 parts per million (ppm) for produced water released into surface waters of the Gulf of Mexico and Pacific Ocean (Fed. Reg. 51, 24897, Jul. 6, 1986).
Other sources of produced water are encountered in the refining of crude oil. Plants which process oil products are increasingly limited by federal and state regulations as to the total organic content (soluble and dispersed hydrocarbons) of effluent water. Additionally, certain production facilities such as steam-generation plants, typically require large amounts of deionized water for processing. Since shortages of freshwater routinely occur in semiarid and desert regions, facilities located in these areas must provide their own source of water.
Older techniques for dealing with contaminated water involved reinjection into wells or percolation through a series of treatment ponds. These methods were unacceptable due to their high costs and environmental damage. Even so, these techniques continue to be used where no economical options exist.
More modern methods of removing oil and water soluble organics from produced water have been previously described. Canadian Patent 1,103,170 relates to the use of a macroreticular, cross-linked polymer adsorbent in columns capable of preferentially adsorbing oil. The patent further relates to the addition of pH adjusting agents coupled with a non-ionic surfactant to remove the adsorbed oil from the column. Additionally, the patent relates to the further alteration of the pH and to the final separation of the oil from the surfactant by phase separation techniques. The method taught by this patent, apart from including several intermediate steps in the purification and recovery process, has the disadvantage of requiring acidification during the processing thereby generating additional pollutants.
Two recent U.S. Pat. Nos. (4,818,410 and 4,839,054) relate to methods for removal of water soluble organics from produced water by acidification, mixing, and phase separation. Similarly to Canadian Patent 1,103,170, these methods include several intermediate steps in the purification and recovery process. Moreover, these patents relate to the use of strong acids, thereby adding pollutants to the process stream.
U.S. Pat. No. 4,775,475 relates to the removal of trace amounts of hydrocarbonaceous compounds from aqueous feedstreams by contacting the feedstream with a suitable adsorbent such as molecular sieves, amorphous silica-alumina gel, silica gel, activated carbon, activated alumina and clays. This patent relates further to the regeneration of these adsorbents by contacting with an elution solvent such as naphtha, kerosene, diesel fuel, gas oil or mixtures of these solvents. In further steps, this patent relates to the treatment of the hydrocarbonaceous compound and elution solvent admixture in the presence of hydrogen with a hydrogenation catalyst, further treatment with an aqueous scrubbing solution which preferably contains a strong base, and still further treatment by phase separation. The resulting spent aqueous scrubbing solution requires neutralization or other treatment prior to releasing into the environment.
One typical method utilized to overcome some of the adverse characteristics of the systems which generate additional pollutants is based upon activated carbon filtration. In an activated carbon system, the carbon must be routinely removed from the filter. After removal, the carbon is either regenerated outside the filter by heating to high temperatures or it is simply discarded and replaced with new material. Additional problems with activated carbon filters arise due to microbial growth on the carbon matrix itself.
More recently, a variety of improved matrices have been designed which overcome some of the limitations encountered with activated carbon, such as the macroreticular resins. Generalized procedures relating to the use of macroreticular resins are also known which are directed to the removal of organics from fluids. See, e.g., U.S. Pat. No. 4,297,220.
In all such systems, a variety of means are taken to monitor the treated produced water in order to ascertain: (1) the efficacy of the treatment procedures; and, (2) the compliance of the treatment with federal and state regulations. Typically, these methods are carried out by spot-checking the effluent treated water by a variety standard methods for examination of water such as Standard Method 5520 B (503 A--Partition-Gravimetric Method) or Standard Method 5520 C (503 B--Partition-Infrared method), see e.g., "Standard Methods for Examination of Water and Waste Water" Port City Press, Baltimore Md, pp. 5-43 to 5-44 (1989).
Again, such methods suffer from a number of disadvantages when used in treatment systems for removal of pollutants from produced water. Chlorinated hydrocarbon solvents as well as strong acids must be added to the water in order to extract the solubilized oil constituents. Furthermore, there is no convenient way in which these methods can be utilized in a continuous monitoring system in order to obviate the necessity of spot-checking filters for the breakthrough level at which point regeneration must be achieved.
Effluent monitoring of oil in water has been accomplished for industrial plant effluents using turbidometers and fluorescence meters, see, e.g. K. Coursin, "Effluent Monitoring for Oil in Water," Pollution Engineering 20:100-102 (1988). However, integrated systems are needed which allow environmentally safe and real-time monitoring of soluble organic concentrations in produced water regardless of salt concentrations in the water. Preferably, such systems will combine a total oil removal process with a system capable of automation which allows continuous monitoring of the efficiency of the purification.
Such improved systems should accurately monitor breakthrough of threshold levels of pollutants which indicate necessity of regeneration of the treatment means regardless of whether this breakthrough occurs as a result of discontinuous oil concentrations in the water to be treated or whether it occurs due to a treatment system failure. Such systems should not be based on time or on volume of effluent but rather they should be based on effluent oil concentration. In addition, such systems should best be automatable such that no human error or down time due to analysis is evident. These requirements are of particular concern where, such as in offshore production operations, alternative methods can dramatically increase costs, waste man-hours and enhance the probability for accidental contamination of the marine environment due to human error.